1. Field of the Invention
The present invention relates generally to encapsulating optically active electronic devices, more particularly to encapsulating such devices mounted on a printed circuit substrate within a pre-formed plastic enclosure having a unitary or a snap-in lens element in one wall thereof for focusing an image on or focusing light from the device.
2. Description of the Prior Art
As electronic optical imaging systems become more compact, particularly with the incorporation of microelectronic photosensor elements for electronic auto exposure systems in relatively compact and inexpensive cameras, it has become desirable to mount the optically active integrated circuit (IC) die on a fiberglass printed circuit board or a ceramic substrate employing chip-on-board technology. The mounting of the optically active IC die directly on or within a recess in a printed circuit board or a substrate allows the inter-connection with its associated circuitry and components to form a relatively compact, flat circuit assembly.
Typically, the optically active semiconductor device is formed as an IC chip containing hundreds or thousands of separate semiconductor devices inter-connected with connection pads to which thin wires extending to printed circuit pads may be bonded. Such a photosensitive IC is disclosed in commonly assigned, U.S. Pat. No. 5,037,198 to Gaboury and incorporated herein by reference. The chip or die itself is characteristically small in size, with dimensions typically on the order of not more than 1/8" by 1/8" square by 0.015" thick. Despite their small size, these chips in accordance with the prior art were typically packaged in supporting structures many times their size, such as in T0-5 cans with wire connection pins extending from the bottom thereof, flat packages with strip connectors extending from the edges thereof, and ceramic or plastic in-line packages with metal prongs extending out of the opposite edges and bent over to form a unit suitable for plugging into a socket or directly into apertures in a printed or hybrid circuit substrate.
Regardless of the particular package utilized for prior art semiconductor chips, including CCD arrays, their primary drawback involves size and cost of separate packaging. On the other hand, the relatively small size packages provide protection from the environment and handling and allow for relatively fail-safe installation.
In order to achieve miniaturization in the entire printed or hybrid circuit comprising the integrated circuit chips and the printed circuit board or substrate, various techniques have been proposed for eliminating the integrated circuit chip package, including mounting the chip or die directly on a prepared region of the substrate or board and encapsulating it in situ with various resins. In commonly assigned U.S. Pat. No. 4,843,036, of which I am a named co-inventor, and with respect to FIG. 1 of that patent, a method is described for encapsulating such optically active integrated circuit chips 20 on a substrate 10 using a transparent encapsulant 32 deposited within a barrier formed around the chip 20. The encapsulant is deposited in a viscous state in the region contained within the barrier 14 and thereafter is cured under ultraviolet light. The cured encapsulant 32 provides a functional, convex lens-like cross-sectional shape to provide focusing of light onto the optically active surface of the integrated device 20 (a photodiode in the disclosed embodiments).
The '036 patent also describes several prior art patents which describe methods for encapsulating electronic devices using radiation curable polymers. U.S. Pat. No. 4,635,356 to Ohuchi et al. describes a method of encapsulating an electronic device wherein a large, free-form spacer is used as a barrier wall to surround electronic components mounted on a radiation-transparent support. The volume within the barrier wall is filled with a radiation curable material to form the finished device.
A further U.S. Pat. No. 4,054,938 to Morris describes the encapsulation of an integrated circuit chip or die. The die carrier is nested into an aperture in the substrate, and an encapsulation material dam provides a four sided enclosure wall placed in contacting engagement with the top surface of the substrate to surround the integrated circuit chip. A thermo-plastic epoxy material is placed over the chip and its attachment wires to pads on the substrate within the region confined by the dam.
One difficulty encountered following the teachings of these references lies in the control of the shape of the curable resin or thermo-plastic epoxy material so that it consistently forms an optical lens suitably shaped to focus an image on the optically active integrated circuit. Earlier systems for enclosing optically active light detectors or light emitters have involved the incorporation of a transparent window or lens within the protective housing for the optically active semi-conductor device in a manner described, for example, in Japanese application number 58-115526 to Watabe, wherein a solid state image pick up device is provided within a package that itself is adapted to be attached to a printed circuit substrate in a manner described above. A lens element is fitted over the optically active surface of the solid-state pick up device and supported by the side walls of the package. Numerous other examples exist of lens and windows mounted on separate packages for optically active integrated circuit chips where the chips or dies are mounted to substrates of the package, and the IC elements are electrically connected to terminal pins which in turn are inserted into connectors mounted to printed circuit boards or substrates.
It also is known from U.S. Pat. Nos. 4,419,722 to Bury and 4,471,414 to Savage to provide snap-in assemblies for holding light emitting diodes (LEDs) in apertures provided in printed circuit boards to both protect and maintain the LED in its proper location.
There remains a need for a miniaturized, flat and thin unitary electronic assembly comprising an integrated circuit chip or die (hereafter referred to collectively or individually as a die) mounted directly to a printed circuit board or hybrid circuit substrate (hereafter referred to collectively and individually as a printed circuit substrate) and provided with a protective lens assembly that is inexpensive and easy to assemble and provides accurate image focusing onto the optically active microelectronic circuit element(s) of the integrated circuit.